Reliability Analysis And Structure Design Of High-density And Large-size Ceramic Column Grid Array Package

With the number and density of I/Os enlarged, CBGA and CCGA are more and more used in electronic packaging. Because of CTE mismatch between ceramic substrate and printed circuit board, the reliability of high I/O CBGA under thermal cycling condition is limited. Since the distance between substrate and board is enlarged, stress and strain level of CCGA from CTE mismatch becomes lower. So the CCGA structure has higher thermomechanical reliability. In allusion to the less of research to reliability of large-size and high-density CCGA at home, how structure factors influencing the fatigue life of CCGA was studied.ANSYS FEM software was utilized to analyse the distributions of stress and strain of 34×34-area-array CCGA with different structure parameters under accelerated thermal cycling condition. Traditional fatigue life prediction equation was used to evaluate the fatigue life of CCGA. The influence of structure factors to reliability of CCGA was analysed based on statistics, and a linear regression fatigue life prediction equation was developed."Daisy chains"to monitor electrical resistance as a failure criterion during the testing, as well as moulds for 2nd level assembly, were designed. Then CCGA structures were assembled for accelerated thermal cycling experiment. The results of FEM and experiment were compared in order to ensure the validity of the finite element models.The results showed that, under accelerated thermal cycling condition, the corner columns of CCGA underwent higher level of stress and strain, and would fail firstly. With the distance from the neutral point (DNP) increased, the level of stress and strain became higher linearly. The stress and strain of solder joints changed periodically under the thermal cycling. Compared with creep strain, plastic strain was low enough to be neglected. Creep strain was the main factor to determine the fatigue life of solder joints. There was stress concentrated at the positions where solder joints connected with PCB, substrate and columns, and cracks would appear firstly at these positions. CTE mismatch between substrate and PCB, pitch between nearest columns and substrate thickness were main structure factors to influence the fatigue life of CCGA. Decreasing CTE mismatch, pitch, substrate thickness and column diameter, as well as increasing column height, would improve the reliability of CCGA. The precision of ceramic substrate, 2nd level assembly procedure, Au/Ni plating thickness, reflow welding procedure would be the reason to the early failure during the testing. Results of the testing were consilient with FEM, ensuring the validity of the finite element models.